Saturday, April 27, 2013

The ground, the ground!

It seems spring has arrived. It was rather coy. It dumped a foot of snow in March, so we had an unusal amount of it around. But "breakup" as they call it in Alaska, seems to have arrived. I know it is breakup when I can see my driveway.
We should not be surprised, but I at least always am. Look! I can see some of the driveway! Behold! I can see the path to the door! We have not beheld this sight since December. The ground is bare. In places. It does seem to be melting. Nights still go below freezing. But we are getting there. Breakup is a frustrating season. Too much snow and slush to bike. Snow quality awful, can't ski. Can't garden. Snow on ground, and it is frozen anyway. Grr. So I have to walk. Trouble is I have taken all walks at least a thousand times. Nothing new here!

Well, there is always clockmaking. It will not be long before I inflict it on you again, so enjoy the respite.

Wednesday, April 17, 2013

Finishing a clock (literally)

The time has come, the walrus said, to speak of many things (Lewis Carrol, The Walrus and the Carpenter). And now we have to put on a spurt of effort and actually finish the thing. Literally. Among the major projects done since my last post, the biggest is the minute work. Clockspeak, of course. In my case this is a misnomer. The Center Wheel revolves at a majestic rate of one revolution per hour. Great thing for a minute hand! But, as you will immediately see, this is not really cool for the hour hand. In one hour, given our 12-hour dials, the hour hand has to go round 1/12 the distance. (12 hours in one half-day). So what to we do? Add more gears, of course. Now I had cut these gears on the bandsaw long ago. But now we have to depth the wheels and pinions.  Clockspeak rears its ugly head again. Remember, big gear is a wheel, small gear is a pinion. Depthing means make them run freely. Book recommends sandpaper. I found a better way. Mr Wilding didn't know about Dremel tools or he would have done this himself. Book published in 2002 or so.
 So I did something I should have done long ago. Live and learn. I measured the aperture between gear teeth, and it is close to or exactly 3mm. I searched my inventory of Dremel tool accessories and found a router bit very close to 3mm. I put the wheel into the Taig and the Dremel into my vertical milling attachment. With this setup I could shave 0.01 mm off the teeth, and shave them I did, running the Dremel at max. Saved hours of work. I used my 60-hole dividing head to position (index) the teeth. Forget sandpaper. It was very nice that these things are 30-tooth gears; my 60-hole dividing plate can handle them easily. Pinions done same way; again they fit my 60-hole dividing plate.

This bit done, the we are almost through the major work on the clock. So the big moment has arrived. The clock was taken apart. If you make a clock, you will soon learn that the fate of a clock is to be taken apart. I handed the clock over to John. He is to make it look pretty. He is very, very, good at that.

 Gulp. The paper patterns have been sanded off. I feel lost without my paper patterns. But go they must. So John got rid of them. My only spec was that the various wheels should have different colors. Here, John is staining the Center Wheel. Previously he has sanded it. Gone is the paper. Again, gulp.
 The plates look very nice in a much darker color. They have a certain character.
There are many details with which we have to deal. But amazing.  A piece of very cheap plywood turns out a very nice clock.

Endless details. I have to smooth out the escape wheel. I have to make the pendulum...  never mind. Progress is progress.

While all this is going on I am setting up to make my next clock. It will not be a wooden clock. And that is all I will say at this point. But clockmaking is not a hobby. It is an obsession.

Wednesday, April 3, 2013

Clock: escaping from reality

If all there were to a clock (wooden or otherwise) were a bunch of gears with a weight (or spring) attached, then it is probably pretty obvious that the falling weight would just unwind the gear train at the proper rate for whatever weight you put on it. Minus friction. So how does a clock keep time? It has to have an escape mechanism, clockspeak for a device that interrupts the weight on its Newton-ordained fall to the ground. The escape mechanism on a clock is usually, in a clock, based on a pendulum; since a pendulum of a given length gives you a very steady beat. But alas, there is friction. You can easily make a pendulum. Put a weight on the end of a rod. Put it in some sort of pivot. A nail, say. Push it. You will see that eventually the pendulum beats no more. Friction, you see. So there is another function the escape mechanism must perform. It has to give a bit of a kick to the pendulum, to counter-act the evil friction. Actually, friction can be a Good Thing (TM) else your car wouldn't stop when you hit the brakes, but in clocks we really, really, don't like it. Again in clockspeak, the bit of a kick is called impulsing the pendulum. Over the years, nay centuries, there have been numerous very clever humans who have designed escape mechanisms, as a Google search on "clock escape mechanisms" will convince you. Mine is what the designers of this clock deemed best, a "deadbeat escape mechanism". There are many others.
The basic escape mechanism consists of the anchor and the pallets.The anchor consists of a piece of wood. You can see the anchor very clearly in the pic above. It looks like an anchor! The pallets are pieces of brass. Resist wear, you see. It was fun making the pallets. I milled them on the lathe, but took no pictures because it was a very simple job. Then I filed to the required angles. Now I have to adjust them, but that will take time (it's a clock!) and I have postponed it. I moved on to that tedious job, the minute work as it is called. The thing is, the clock is set up (all those gears!) so the Center Wheel (one of the gears) revolves at 1/60 times a second, or in other words one minute. But there is an hour hand. It must go around the dial much slower than the minute hand. In fact it must go around 60 times slower. (assuming you have a 12-hour dial). More gears. That's what the minute work is for. Another gearbox. Now the wheels were cut out on a bandsaw by hand. Hardly precision work. Furthermore here are small imperfections caused by the fact that you did not drill the holes for the axles, or arbors, exactly where you should. So we have to depth the gears (wheels). In this clock, says Mr Wilding, this involves sanding off bits from the teeth until the gears spin freely. At first I tried sandpaper. Very slow. I spent three days depthing the wheels. Then I got smart. I rigged up my lathe with it Dremel milling jig, which I described elsewhere.

The Dremel has a router bit in it. With this baby I can take off as little as .01 cm (or .0005") at  one go from the wheel. (Not really. This is wood, not metal. Precision is futile). This speeded up the problem considerably. Couldn't have done this with the going train (the main gears) because the wheels are too big to "swing" on my little Taig. Later I got even smarter. But that's another post. Live and learn.